Human papillomavirus (HPV) is a virus that causes verrucae, or warts, on the skin, particularly of the distal extremities, and lesions of the mucous membranes. Warts are highly prevalent, occurring in up to 13% of the general population and in around 25% of otherwise healthy children. About 67% of warts resolve spontaneously within two years; however more than 25% will persist for many years, some resulting in pain or dysfunction and some imparting significant psychosocial problems. Localized hyperthermia (warming) has been reported to be effective in the treatment of HPV-induced warts for nearly two decades. A novel method of treating warts with heat is the use of an occlusive patch that contains a mixture of chemicals (ferric chloride), which in the presence of oxygen reacts to generate reproducible thermal warming of the skin to a temperature of 42-43ºC for at least two hours. The heat is believed to alter the immune response and kill the HPV virus in the wart tissue.